The overall objective is to test whether an alteration in the molecular composition or molecular ordering of extracellular macromolecules (ECM) constitutes a principal underlying factor predisposing an embryo to defects in craniofacial (CF) development. The problem analysis focuses on the neural crest progenitor of CF tissue and asks the following questions: (1) What is the chemical nature of the abundant amorphous extracellular material which surrounds migrating cephalic neural crest cells and CF primordia? (2) Does any particular spatial ordering (molecular packaging) of the matrical substances impart instructive or regulatory information on cephalic neural crest migration or determination? (3) Do any of the extracellular substances (individually or in combination) have direct inductive influences on the phenotypic transformation of cephalic neural crest into the mesenchymal derivatives of CF primordia? In both chick and rat embryos, identification and distribution of ECM (correlated to the movement of migrating crest cells) will be based on transmission and scanning EM analyses of fixed or carbon platinum replicas of frozen-dried cephalic primordia exposed to specific enzymic or extractive techniques and alcian blue, lectin, dialyzed iron, or immunocytochemical staining or x-ray detection of sulfur emission matrix inhibitors (Diazo-5 oxo-L-Norleucine for glycosaminoglycans and azetidine for collagen) together with lysozyme and Beta-aminoproprionitrile will be used to evaluate the significance of molecular ordering (the latter two agents disrupt inter-molecular associations without directly affecting short term cell synthesis). Individual compositional contributions of the various matrical macromolecules to the morphogenesis of CF primordia will be tested in two and three dimensional tissues of normal plate or cephalic mesenchyme explants. Individual moieties or combinations of varying ratios of matrix moieties will be added for the culture medium or incorporated into substrates on which the cells are grown. Data should indicate if matrix organization and composition are directly related to CF development and if microenvironmental alterations in CF constitute a molecular pathway of abnormal CF development.